NB LTE PRACH design

ABSTRACT

A method in a user equipment is disclosed. The method comprises generating a narrowband random access preamble for a narrowband random access procedure, the narrowband random access preamble comprising a Zadoff-Chu sequence. The method comprises transmitting, to a network node, the generated narrowband random access preamble via a narrowband physical random access channel (PRACH) according to a narrowband PRACH format, wherein the narrowband PRACH is frequency multiplexed with a physical uplink shared channel (PUSCH) and comprises: at least one narrowband PRACH slot having a narrowband PRACH slot duration; and a narrowband PRACH period.

PRIORITY

This nonprovisional application is a continuation of U.S. Nonprovisionalapplication Ser. No. 16/708,832, filed Dec. 10, 2019, which is acontinuation of U.S. Nonprovisional application Ser. No. 15/747,503,filed Jan. 25, 2018, now U.S. Pat. No. 10,554,366, which is a 35 U.S.C.§ 371 of International Patent Application No. PCT/IB2016/054399, filedJul. 22, 2016, and entitled “NB LTE PRACH Design” which claims priorityto U.S. Provisional Patent Application No. 62/197,374, filed Jul. 27,2015, the disclosures of which are hereby incorporated by reference intheir entirety.

TECHNICAL FIELD

The present disclosure relates, in general, to wireless communicationsand, more particularly, to narrowband Long Term Evolution PhysicalRandom Access Channel design.

BACKGROUND

The Internet of Things (IoT) is a vision for the future where everythingthat can benefit from a connection will be connected. Cellulartechnologies are being developed or evolved to play an indispensablerole in the IoT world, particularly machine-type-communication (MTC).MTC is characterized by lower demands on data rates than, for example,mobile broadband, but with higher requirements on low cost devicedesign, better coverage, and the ability to operate for years onbatteries without charging or replacing the batteries. To meet the IoTdesign objectives, 3GPP is currently studying the evolutions of existing2G/3G/4G Long Term Evolution (LTE) technologies. The current studiesunder GSM/EDGE Radio Access Network (GERAN) include both Global Systemfor Mobile communications (GSM) evolution and completely new designs.

There are two main so-called “Clean Slate” solutions: (i) Narrowband(NB) Machine-to-Machine (M2M) and (ii) NB Orthogonal Frequency DivisionMultiple Access (OFDMA). Recently, a merged solution called NB CellularIoT (CIoT) with NB M2M uplink and NB OFDMA downlink has been proposedand studied in GERAN. These Clean Slate solutions are NB systems with acarrier bandwidth of 200 kHz. The Clean Slate solutions target improvedcoverage compared to today's GSM systems, long battery life, and lowcomplexity communication design. One intention with the Clean Slatesolutions is to deploy them in spectrum that is currently used for GSM,which can be achieved by reducing the bandwidth used by GSM anddeploying NB Clean Slate systems in the spectrum that becomes available.Another intention is to reuse existing GSM sites for the deployment ofNB Clean Slate systems. 3GPP has decided to move the work on specifyingan NB MTC solution from GERAN to RAN.

In existing LTE random access design, random access serves multiplepurposes. These purposes include initial access when a user equipment(UE) establishes a radio link, scheduling request, etc. Among others, amain objective of random access is to achieve uplink (UL)synchronization, which is important for maintaining the UL orthogonalityin LTE. LTE random access can be either contention-based orcontention-free. The contention-based random access procedure consistsof four steps:

1) From UE to eNB: Random access preamble;

2) From eNB to UE: Random access response;

3) From UE to eNB: Scheduled transmission; and

4) From eNB to UE: Contention resolution.

Note that only Step 1 involves physical-layer processing specificallydesigned for random access. The remaining three steps (Steps 2-4) followthe same physical-layer processing used in UL and downlink (DL) datatransmission. For contention-free random access, the UE uses reservedpreambles assigned by the base station. In this case, contentionresolution is not needed, and thus only Steps 1 and 2 are required.

In LTE, random access preambles are sent in the Physical Random AccessChannel (PRACH). The PRACH subcarrier spacing is 1.25 kHz, and thepreambles are Zadoff-Chu sequences of length 839. A fixed number ofpreambles (64) are available in each LTE cell. Several preamble formatsof different durations of the sequence and cyclic prefix are defined tobe used for cells of different sizes. The format configured in a cell isbroadcast in the System Information.

One prominent feature of NB LTE is in-band operation (i.e., NB LTE canbe deployed within a wideband LTE subcarrier by puncturing one physicalresource block (PRB) in the LTE carrier and using it for NB LTEtransmission). To enable this in-band operation, it is important tosynthesize the NB LTE numerologies with legacy LTE to avoid mutualinterference between NB LTE and legacy LTE as much as possible.

In NB LTE, the random access procedure follows its counterpart in LTE.Due to the reduced bandwidth in NB LTE, however, LTE PRACH design cannotbe directly applied to NB LTE. As noted above, the LTE PRACH subcarrierspacing is 1.25 kHz and the preambles are Zadoff-Chu sequences of length839. Thus, the total used bandwidth is 1.0488 MHz (excluding guardband). In contrast, NB LTE is designed to operate with a carrierbandwidth of 200 kHz (more precisely, the usable bandwidth is 180 kHz),making LTE PRACH design inapplicable to NB LTE.

Another relevant consideration is the subcarrier spacing for thePhysical Uplink Shared Channel (PUSCH) in NB LTE. In NB LTE, PUSCH mayhave any suitable subcarrier spacing. As one example, in NB LTE thesubcarrier spacing for PUSCH can be 2.5 kHz, which is reduced by 6 timescompared to the 15 kHz subcarrier spacing of LTE. One approach to PRACHdesign for NB LTE would be to reduce the 1.25 kHz subcarrier spacing by6 times and reuse the length-839 Zadoff-Chu sequences. There are,however, several problems with this design. First, the reducedsubcarrier spacing is 208.3 Hz, which is relatively small consideringthe frequency offset between the device and base station and Dopplershift. Second, the total used bandwidth for PRACH would be 174.8 kHz(208.3*839=174.8 kHz), while the total uplink bandwidth is 180 kHz in NBLTE. As a result, at most two 2.5 kHz subcarriers can be used for PUSCH,and there is no guard band between PUSCH and PRACH when they arefrequency multiplexed. As a result, the PUSCH capacity for continuouspacket transmissions of users in bad coverage may be limited.Furthermore, different durations of the sequence and cyclic prefix areneeded to support cells of different sizes in LTE. This requires moreinformation to be broadcast in System Information. Thus, there is a needfor an improved PRACH design for NB LTE.

SUMMARY

To address the foregoing problems with existing approaches, disclosed isa method in a user equipment. The method comprises generating anarrowband random access preamble for a narrowband random accessprocedure, the narrowband random access preamble comprising a Zadoff-Chusequence. The method comprises transmitting, to a network node, thegenerated narrowband random access preamble via a narrowband physicalrandom access channel (PRACH) according to a narrowband PRACH format,wherein the narrowband PRACH is frequency multiplexed with a physicaluplink shared channel (PUSCH) and comprises: at least one narrowbandPRACH slot having a narrowband PRACH slot duration; and a narrowbandPRACH period.

In certain embodiments, the narrowband random access preamble may be aZadoff-Chu sequence of length 491. The generated narrowband randomaccess preamble may comprise a duration of 3.2 ms, and the narrowbandPRACH may comprise a cyclic prefix of 0.4 ms and a guard time of 0.4 ms.The narrowband PRACH may comprise a subcarrier spacing of 312.5 Hz. Thenarrowband PRACH may comprise at least one subcarrier guard band betweenthe PRACH and the PUSCH. The narrowband PRACH slot duration and thenarrowband PRACH period may be based on one or both of: a cell load of acell associated with the network node; and a cell size of the cellassociated with the network node. The narrowband PRACH slot duration maybe 12 ms.

In certain embodiments, the narrowband PRACH slot may comprise at leastone narrowband PRACH segment. The method may comprise randomly selectingone of a plurality of possible narrowband random access preambles as thenarrowband random access preamble to generate. The method may compriserandomly selecting one of the at least one narrowband PRACH segments fortransmitting the selected one of the plurality of possible narrowbandrandom access preambles.

In certain embodiments, the method may comprise determining a coveragelevel of the user equipment, and selecting, based on the determinedcoverage level of the user equipment, the narrowband PRACH format fromamong one or more narrowband PRACH formats. The coverage level of theuser equipment may comprise one or more of a basic coverage level, arobust coverage level, and an extreme coverage level. The method maycomprise repeating transmission of the narrowband random access preambleaccording to the selected narrowband PRACH format.

Also disclosed is a user equipment. The user equipment comprises one ormore processors. The one or more processors are configured to generate anarrowband random access preamble for a narrowband random accessprocedure, the narrowband random access preamble comprising a Zadoff-Chusequence. The one or more processors are configured to transmit, to anetwork node, the generated narrowband random access preamble via anarrowband physical random access channel (PRACH) according to anarrowband PRACH format, wherein the narrowband PRACH is frequencymultiplexed with a physical uplink shared channel (PUSCH) and comprises:at least one narrowband PRACH slot having a narrowband PRACH slotduration; and a narrowband PRACH period.

Also disclosed is a method in a network node. The method comprisesconfiguring, based on one or more criteria, a narrowband physical randomaccess channel (PRACH) slot duration and a narrowband PRACH period for anarrowband random access procedure by a user equipment. The methodcomprises receiving, from the user equipment, a narrowband random accesspreamble via a narrowband PRACH according to a narrowband PRACH format,wherein the narrowband random access preamble comprises a Zadoff-Chusequence, and wherein the narrowband PRACH is frequency multiplexed witha physical uplink shared channel (PUSCH) and comprises: at least onenarrowband PRACH slot having the configured narrowband PRACH slotduration; and the configured narrowband PRACH period.

In certain embodiments, the narrowband random access preamble may be aZadoff-Chu sequence of length 491. The received narrowband random accesspreamble may comprise a duration of 3.2 ms. The narrowband PRACH maycomprise a cyclic prefix of 0.4 ms and a guard time of 0.4 ms. Thenarrowband PRACH may comprise a subcarrier spacing of 312.5 Hz. Thenarrowband PRACH may comprise at least one subcarrier guard band betweenthe narrowband PRACH and the PUSCH. The one or more criteria maycomprise one or more of: a cell load of a cell associated with thenetwork node; and a cell size of the cell associated with the networknode. The configured narrowband PRACH slot duration may be 12 ms.

In certain embodiments, the narrowband PRACH slot may comprise at leastone narrowband PRACH segment. The method may comprise configuring theuser equipment to randomly select one of a plurality of possiblenarrowband random access preambles to generate, and configuring the userequipment to randomly select one of the at least one narrowband PRACHsegments for transmitting the selected one of the plurality of possiblenarrowband random access preambles.

In certain embodiments, the method may comprise determining thenarrowband PRACH format according to which the narrowband random accesspreamble was received, and determining a coverage level of the userequipment based on the determined narrowband PRACH format. The coveragelevel of the user equipment may comprise one or more of a basic coveragelevel, a robust coverage level, and an extreme coverage level. Thenarrowband PRACH format according to which the narrowband random accesspreamble was received may be determined based on a number of repeattransmissions of the narrowband random access preamble. In certainembodiments, the method may comprise scheduling the user equipmentaccording to the determined coverage level of the user equipment.

Also disclosed is a network node. The network node comprises one or moreprocessors. The one or more processors are configured to configure,based on one or more criteria, a narrowband physical random accesschannel (PRACH) slot duration and a narrowband PRACH period for anarrowband random access procedure by a user equipment. The one or moreprocessors are configured to receive, from the user equipment, anarrowband random access preamble via a narrowband PRACH according to anarrowband PRACH format, wherein the narrowband random access preamblecomprises a Zadoff-Chu sequence, and wherein the narrowband PRACH isfrequency multiplexed with a physical uplink shared channel (PUSCH) andcomprises: at least one narrowband PRACH slot having the configurednarrowband PRACH slot duration; and the configured narrowband PRACHperiod.

Certain embodiments of the present disclosure may provide one or moretechnical advantages. As one example, certain embodiments may allow forflexible PUSCH and PRACH multiplexing, which may advantageously enablecontinuous packet transmissions of users in bad coverage. As anotherexample, certain embodiments may include carefully selected subcarrierspacing and preamble length. This may advantageously enhance PRACHdetection performance, enable the 164 dB maximum coupling loss target tobe met, and enable satisfactory time-of-arrival estimation at the basestations. As still another example, in certain embodiments the PRACHdesign is flexible and can be configured based on one or more of cellsize and system load. As yet another example, in certain embodiments thePRACH design fits well within the overall frame structure of NB LTE, andcan advantageously be used to distinguish users in different coverageclasses. As yet another example, in certain embodiments well-designedcyclic prefix and guard period structure may advantageously enable asingle configuration to support cell sizes up to 60 km. Other advantagesmay be readily apparent to one having skill in the art. Certainembodiments may have none, some, or all of the recited advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed embodiments and theirfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an example embodiment of a wireless communicationsnetwork, in accordance with certain embodiments;

FIG. 2 illustrates an example of PRACH multiplexing with PUSCH in NBLTE, in accordance with certain embodiments;

FIG. 3 illustrates an example design of PRACH preamble length andsubcarrier spacing, in accordance with certain embodiments;

FIG. 4 illustrates an example of PRACH cyclic prefix and guard perioddimensioning, in accordance with certain embodiments;

FIG. 5 is a flow diagram of a method in a user equipment, in accordancewith certain embodiments;

FIG. 6 is a flow diagram of a method in a network node, in accordancewith certain embodiments;

FIG. 7 is a block schematic of an exemplary wireless device, inaccordance with certain embodiments;

FIG. 8 is a block schematic of an exemplary network node, in accordancewith certain embodiments;

FIG. 9 is a block schematic of an exemplary radio network controller orcore network node, in accordance with certain embodiments;

FIG. 10 is a block schematic of an exemplary wireless device, inaccordance with certain embodiments; and

FIG. 11 is a block schematic of an exemplary network node, in accordancewith certain embodiments.

DETAILED DESCRIPTION

As described above, due to the reduced bandwidth in NB LTE, the LTEPRACH design cannot be directly applied to NB LTE. Existing approachesfor enabling a NB LTE PRACH design, which use reduced subcarrier spacingand reuse the length-839 Zadoff-Chu sequences of the LTE PRACH design,suffer from certain deficiencies. Namely, the reduced subcarrier spacingof the existing approach is relatively small considering the frequencyoffset between the device and base station and Doppler shift.Furthermore, the total bandwidth used would limit the bandwidth thatcould be used for PUSCH, and would provide no guard band between PUSCHand PRACH when they are frequency multiplexed. This may limit PUSCHcapacity for continuous packet transmissions of users in bad coverage.

The present disclosure contemplates various embodiments that may addressthese and other deficiencies associated with existing approaches to NBLTE PRACH design. In certain embodiments, a novel orthogonal frequencydivision multiplexing (OFDM) PRACH design for NB LTE is proposed. Thegeneral design principles follow those of LTE, but novel modificationsare proposed to adapt the LTE PRACH design to NB LTE, which operateswith a much reduced 200 kHz bandwidth. In certain embodiments, theproposed PRACH design uses 160 kHz bandwidth in the uplink, leaving 20kHz bandwidth for continuous uplink packet transmissions. New subcarrierspacing is proposed for generating random access preambles, and a newset of Zadoff-Chu sequences are proposed as preambles for random accessin NB systems. In certain embodiments, 312.5 Hz subcarrier spacing andlength-491 Zadoff-Chu sequences for preambles are used, which strikes agood balance between robustness to carrier frequency offset/Dopplershift and maximizes the number of orthogonal preambles for the NB LTEsystems. In certain embodiments, the PUSCH and PRACH are frequencymultiplexed to allow continuous uplink traffic transmission. The cyclicprefix and guard period are carefully dimensioned to maximize coverage.In certain embodiments, this may enable a single configuration to beapplicable to cells of sizes up to 60 km. The design described hereinmay also allow multiple random access segments to be configured in thesame random access slot, facilitating coherent combination of receivedpreambles over consecutive segments transmitted by users in badcoverage. In addition, different random access formats can be used byusers in different coverages, from which base stations (such as eNBs)can implicitly derive users' coverage classes and make schedulingdecisions accordingly. The design described herein also may enable jointrandom preamble selection and random segment selection, which helpsreduce random access collision rate.

According to one example embodiment, a method in a UE is disclosed. Themethod may comprise generating a NB random access preamble for a NBrandom access procedure, the NB random access preamble comprising aZadoff-Chu sequence. The method may comprise transmitting, to a networknode, the generated NB random access preamble via a NB PRACH accordingto a NB PRACH format, wherein the NB PRACH is frequency multiplexed withPUSCH and comprises: at least one NB PRACH slot having a NB PRACH slotduration; and a NB PRACH period.

According to another example embodiment, a method in a network node isdisclosed. The method may comprise configuring, based on one or morecriteria, a NB PRACH slot duration and a NB PRACH period for a NB randomaccess procedure by a UE. The method may comprise receiving, from theUE, a NB random access preamble via a NB PRACH according to a NB PRACHformat, wherein the NB random access preamble comprises a Zadoff-Chusequence, and wherein the NB PRACH is frequency multiplexed with PUSCHand comprises: at least one NB PRACH slot having the configured NB PRACHslot duration; and the configured NB PRACH period.

The various embodiments described herein may provide one or moretechnical advantages. As one example, certain embodiments may allow forflexible PUSCH and PRACH multiplexing, which may advantageously enablecontinuous packet transmissions of users in bad coverage. As anotherexample, certain embodiments may include carefully selected subcarrierspacing and preamble length. This may advantageously enhance PRACHdetection performance, enable the 164 dB maximum coupling loss target tobe met, and enable satisfactory time-of-arrival estimation at the basestations (e.g., eNBs). As still another example, in certain embodimentsthe PRACH design is flexible and can be configured based on one or moreof cell size and system load. As yet another example, in certainembodiments the PRACH design fits well within the overall framestructure of NB LTE, and can advantageously be used to distinguish usersin different coverage classes. As yet another example, in certainembodiments well-designed cyclic prefix and guard period structure mayadvantageously enable a single configuration to support cell sizes up to60 km. Other advantages may be readily apparent to one having skill inthe art. Certain embodiments may have none, some, or all of the recitedadvantages.

FIG. 1 is a block diagram illustrating an embodiment of a network 100,in accordance with certain embodiments. Network 100 includes one or moreUE(s) 110 (which may be interchangeably referred to as wireless devices110) and one or more network node(s) 115 (which may be interchangeablyreferred to as eNBs 115). UEs 110 may communicate with network nodes 115over a wireless interface. For example, a UE 110 may transmit wirelesssignals to one or more of network nodes 115, and/or receive wirelesssignals from one or more of network nodes 115. The wireless signals maycontain voice traffic, data traffic, control signals, and/or any othersuitable information. In some embodiments, an area of wireless signalcoverage associated with a network node 115 may be referred to as acell. In some embodiments, UEs 110 may have device-to-device (D2D)capability. Thus, UEs 110 may be able to receive signals from and/ortransmit signals directly to another UE.

In certain embodiments, network nodes 115 may interface with a radionetwork controller. The radio network controller may control networknodes 115 and may provide certain radio resource management functions,mobility management functions, and/or other suitable functions. Incertain embodiments, the functions of the radio network controller maybe included in network node 115. The radio network controller mayinterface with a core network node. In certain embodiments, the radionetwork controller may interface with the core network node via aninterconnecting network. The interconnecting network may refer to anyinterconnecting system capable of transmitting audio, video, signals,data, messages, or any combination of the preceding. The interconnectingnetwork may include all or a portion of a public switched telephonenetwork (PSTN), a public or private data network, a local area network(LAN), a metropolitan area network (MAN), a wide area network (WAN), alocal, regional, or global communication or computer network such as theInternet, a wireline or wireless network, an enterprise intranet, or anyother suitable communication link, including combinations thereof.

In some embodiments, the core network node may manage the establishmentof communication sessions and various other functionalities for UEs 110.UEs 110 may exchange certain signals with the core network node usingthe non-access stratum layer. In non-access stratum signaling, signalsbetween UEs 110 and the core network node may be transparently passedthrough the radio access network. In certain embodiments, network nodes115 may interface with one or more network nodes over an internodeinterface, such as, for example, an X2 interface.

As described above, example embodiments of network 100 may include oneor more UEs 110, and one or more different types of network nodescapable of communicating (directly or indirectly) with UEs 110.

In some embodiments, the non-limiting term UE is used. UEs 110 describedherein can be any type of wireless device capable of communicating withnetwork nodes 115 or another UE over radio signals. UE 110 may also be aradio communication device, target device, D2D UE,machine-type-communication UE or UE capable of machine to machinecommunication (M2M), low-cost and/or low-complexity UE, a sensorequipped with UE, Tablet, mobile terminals, smart phone, laptop embeddedequipped (LEE), laptop mounted equipment (LME), USB dongles, CustomerPremises Equipment (CPE), etc. UE 110 may operate under either normalcoverage or enhanced coverage with respect to its serving cell. Theenhanced coverage may be interchangeably referred to as extendedcoverage. UE 110 may also operate in a plurality of coverage levels(e.g., normal coverage, basic coverage, robust coverage, extremecoverage, enhanced coverage level 1, enhanced coverage level 2, enhancedcoverage level 3 and so on). In some cases, UE 110 may also operate inout-of-coverage scenarios.

Also, in some embodiments generic terminology, “radio network node” (orsimply “network node”) is used. It can be any kind of network node,which may comprise a base station (BS), radio base station, Node B, basestation (BS), multi-standard radio (MSR) radio node such as MSR BS,evolved Node B (eNB), network controller, radio network controller(RNC), base station controller (BSC), relay node, relay donor nodecontrolling relay, base transceiver station (BTS), access point (AP),radio access point, transmission points, transmission nodes, RemoteRadio Unit (RRU), Remote Radio Head (RRH), nodes in distributed antennasystem (DAS), Multi-cell/multicast Coordination Entity (MCE), corenetwork node (e.g., MSC, MME, etc.), O&M, OSS, SON, positioning node(e.g., E-SMLC), MDT, translation node (e.g., PLAT) or any other suitablenetwork node.

The terminology such as network node and UE should be considerednon-limiting and does in particular not imply a certain hierarchicalrelation between the two; in general “eNodeB” could be considered asdevice 1 and “UE” device 2, and these two devices communicate with eachother over some radio channel.

Example embodiments of UE 110, network nodes 115, and other networknodes (such as radio network controller or core network node) aredescribed in more detail below with respect to FIGS. 7-11 .

Although FIG. 1 illustrates a particular arrangement of network 100, thepresent disclosure contemplates that the various embodiments describedherein may be applied to a variety of networks having any suitableconfiguration. For example, network 100 may include any suitable numberof UEs 110 and network nodes 115, as well as any additional elementssuitable to support communication between UEs or between a UE andanother communication device (such as a landline telephone).Furthermore, although certain embodiments may be described asimplemented in a Long Term Evolution (LTE) network, the embodiments maybe implemented in any appropriate type of telecommunication systemsupporting any suitable communication standards (including 5G standards)and using any suitable components, and are applicable to any radioaccess technology (RAT) or multi-RAT systems in which a UE receivesand/or transmits signals (e.g., data). For example, the variousembodiments described herein may be applicable to LTE, LTE-Advanced, 5G,UMTS, HSPA, GSM, cdma2000, WCDMA, WiMax, UMB, WiFi, another suitableradio access technology, or any suitable combination of one or moreradio access technologies. Although certain embodiments may be describedin the context of wireless transmissions in the downlink, the presentdisclosure contemplates that the various embodiments are equallyapplicable in the uplink.

As described above, due to the reduced bandwidth of NB LTE, legacy LTEPRACH design cannot be reused in NB LTE. Compared to the existingdesign, the new NB LTE PRACH design described herein allows for flexiblePUSCH and PRACH multiplexing, provides enhanced PRACH detectionperformance, enables configurable formats based on cell size and/orsystem load, fits well within the overall frame structure of NB LTE, andsupports users of different coverage classes. Various features of thenew NB LTE PRACH design are described below in relation to FIGS. 2-4 ,including multiplexing of PRACH with PUSCH, preamble design, and PRACHdimensioning.

FIG. 2 illustrates an example of PRACH multiplexing with PUSCH in NBLTE, in accordance with certain embodiments. More particularly, FIG. 2illustrates a time-frequency grid having three PRACH periods 205. EachPRACH period 205 includes a PRACH slot 210 and PUSCH 215. PRACH periods205, PRACH slots 210, and PUSCH 215 may have any suitable duration. Inthe example of FIG. 2 , each PRACH period 205 has a duration of 60 ms,and each PRACH slot 210 has a duration of 12 ms.

PRACH time-frequency resources can be configured in any suitable manner.For example, in certain embodiments PRACH time-frequency resources canbe configured by a base station, such as eNB 115 described above inrelation to FIG. 1 . The time-frequency resources configuration candepend on any suitable factors. For example, in certain embodiments thetime-frequency resources configuration may depend on one or more of therandom access load, the cell size, or any other suitable factor. Notethat PUSCH 215 can still be frequency multiplexed with PRACH in PRACHslots 210. This design is motivated by the fact that users in badcoverage may require a long time to finish their packet transmissions.Thus, in certain embodiments some edge subcarriers are reserved forPUSCH, which may advantageously allow continuous traffic transmissionsof wireless devices (such as wireless device 110 describe above inrelation to FIG. 1 ) in bad coverage, given that the wireless devicesare scheduled on the edge subcarriers.

FIG. 3 illustrates an example design of PRACH preamble length andsubcarrier spacing, in accordance with certain embodiments. Moreparticularly, FIG. 3 illustrates PRACH 305, a pair of guard bands 310,and PUSCH 315. PRACH 305 is made up of a plurality of subcarriers 320.PRACH 305, guard bands 310, PUSCH 315, and subcarriers 320 may have anysuitable dimensions. In the example embodiment of FIG. 3 , PRACH 305includes 491 PRACH subcarriers 320, with each PRACH subcarrier 320having a size of 312.5 Hz. Each guard band 310 is made up of 10.5subcarriers, each having a size of 312.5 Hz. Each PUSCH 315 is made upof four subcarriers, each subcarrier having a size of 2.5 kHz.

In certain embodiments, a portion of the bandwidth is reserved for PUSCH315. This may advantageously allow for continuous uplink packettransmission. The amount of bandwidth reserved for PUSCH 315 may varyaccording to particular implementations. As one example, in certainembodiments eight 2.5 kHz edge subcarriers are reserved for PUSCH 315(four on either side of guard bands 310). This leaves 160 kHz bandwidthfor PRACH 305. On the one hand, large subcarrier spacing is desirable inorder to make the preamble transmission robust to carrier frequencyoffset and Doppler shift. On the other hand, longer Zadoff-Chu sequencebased preambles are preferred. This is because orthogonal preambles arederived by applying cyclic shifts to a base Zadoff-Chu sequence. For agiven cell size (i.e., a given cyclic shift), the longer the preambles,the more orthogonal the preambles. With 160 kHz bandwidth for PRACH 305,a tradeoff exists between PRACH subcarrier spacing and preamble length.Further, the choice should enable PRACH to fit well within the overallframe structure in NB LTE.

Taking into account all the constraints, the example embodimentillustrated in FIG. 3 reduces the 1.25 kHz LTE PRACH subcarrierbandwidth by four times for NB LTE PRACH 305 (i.e., subcarrier spacingof 312.5 Hz). It is important to leave some guard band between PUSCH 315and PRACH 305 to mitigate their mutual interference. Reserving about onedata subcarrier guard band is required between PRACH 305 and PUSCH 315.Therefore, the actually used bandwidth for NB LTE PRACH in the exampleembodiment of FIG. 3 is 155 kHz. Thus, the maximum preamble length is496 (155/0.3125=496). To maximize the number of potential preambles thathave good cross-correlation property, Zadoff-Chu sequence length isselected to be prime. The largest prime number less than 496 is 491.Therefore, in the example embodiment of FIG. 3 length-491 Zadoff-Chusequences are used as preambles. The length-491 Zadoff-Chu sequences aremapped to 312.5 Hz spaced subcarriers.

FIG. 4 illustrates an example of PRACH cyclic prefix and guard perioddimensioning, in accordance with certain embodiments. More particularly,FIG. 4 illustrates two scenarios 405A and 405B over the course of onePRACH slot 410. In scenario 405A, the UE (such as UE 110 described abovein relation to FIG. 1 ) is close to the eNB (such as eNB 115 describedabove in relation to FIG. 1 ). In scenario 405B, the UE is close to celledge. For each of scenarios 405A and 405B, the cyclic prefix 415,preamble sequence 420, and guard time 425 are illustrated.

The duration of PRACH slot 410 and the PRACH period can be configureddepending on any suitable factors. For example, in certain embodimentsthe duration of PRACH slot 410 and the PRACH period can be configureddepending on the load and cell size. FIG. 4 illustrate one exampleconfiguration.

In the example embodiment of FIG. 4 , with 312.5 Hz subcarrier spacing,preamble sequence 420 has a duration of 3.2 ms. In the exampleconfiguration of FIG. 4, PRACH slot 410 has a duration of 12 ms. Each 12ms PRACH slot 410 is further divided into three 4 ms PRACH segments 430.Since the duration of preamble sequence 420 is 3.2 ms, there are 0.8 msresources remaining for cyclic prefix 415 and guard time 425. In theexample embodiment of FIG. 4 , the cyclic prefix is dimensioned to be0.4 ms to maximize coverage (ignoring the delay spread, which is on theorder of a few μs and has marginal impact).

In the example embodiment of FIG. 4 , cyclic prefix 415 having aduration of 0.4 ms can address cell sizes up to 60 km. Also, with 512point IFFT for PRACH preamble generation, the size of cyclic prefix 415amounts to 64 samples, making adding cyclic prefix straightforward inbaseband processing. Though preambles are defined in frequency domain,devices (such as wireless device 110 described above in relation to FIG.1 ) can directly generate the preambles in time domain and can thereforebypass the 512 point IFFT operation. Moreover, Zadoff-Chu sequences haveconstant amplitude, leading to minimal requirements on power amplifiersof low cost MTC devices.

Based on the cyclic prefix and guard time dimensioning described abovein relation to FIG. 4 , three example PRACH formats are defined in Table1 below. Although the example of Table 1 includes three PRACH formats,the present disclosure contemplates that any suitable number of PRACHformats may be used, and the number of PRACH formats may vary accordingto particular implementations. In the example of Table 1, Formats 0, 1,and 2 are respectively used by users in basic, robust, and extremecoverage in NB LTE. As used herein, the basic, robust, and extremecoverage levels refer generally to three different coverage levels. Incases where more or less than three PRACH formats are used, greater orfewer coverage levels may be defined. The specifics of each coveragelevel may vary according to particular implementations. As one example,in certain embodiments basic coverage is defined with respect totraditional GSM/GPRS network coverage (i.e., 144 dB), robust coverageyields +10 dB coverage extension (i.e., 154 dB), and extreme coverageyields +20 dB coverage extension (i.e., 164 dB). In such a case, networkcoverage refers to what extent the network can reach the devices. Forexample, extreme coverage (i.e., 164 dB) may allow the network to reachdevices, such as wireless device 110 described above, that are located,for example, in a deep basement. Note that the formats in Table 1 areexamples; detailed numbers of repetitions can vary.

TABLE 1 PRACH formats Tcp Tseq Format (ms) (ms) repetitions 0 0.4 3.2 11 0.4 3.2 6 2 0.4 3.2 18For users in basic coverage (using Format 0 in Table 1 above), one PRACHsegment is sufficient to send their preambles. As there are threesegments per 12 ms PRACH slot, users in basic coverage can randomlychoose one of the three segments, tripling the random access capacity.For users in robust coverage (using Format 1 in Table 1 above), eachpreamble transmission is repeated six times and thus occupies two 12 msPRACH slots. For users in extreme coverage (using Format 2 in Table 1above), each preamble transmission is repeated 18 times and thusrequires six 12 ms PRACH slots.

FIG. 5 is a flow diagram of a method 500 in a user equipment, inaccordance with certain embodiments. The method begins at step 504,where the user equipment generates a narrowband random access preamblefor a narrowband random access procedure, the narrowband random accesspreamble comprising a Zadoff-Chu sequence. In certain embodiments, thenarrowband random access preamble may be a Zadoff-Chu sequence of length491. The generated narrowband random access preamble may comprise aduration of 3.2 ms.

At step 508, the user equipment transmits, to a network node, thegenerated narrowband random access preamble via a narrowband physicalrandom access channel (PRACH) according to a narrowband PRACH format,wherein the narrowband PRACH is frequency multiplexed with a physicaluplink shared channel (PUSCH) and comprises: at least one narrowbandPRACH slot having a narrowband PRACH slot duration; and a narrowbandPRACH period. In certain embodiments, the narrowband PRACH may comprisea subcarrier spacing of 312.5 Hz. The narrowband PRACH may comprise atleast one subcarrier guard band between the PRACH and the PUSCH. Thenarrowband PRACH slot duration and the narrowband PRACH period may bebased on one or both of: a cell load of a cell associated with thenetwork node; and a cell size of the cell associated with the networknode. The narrowband PRACH slot duration may be 12 ms. The narrowbandPRACH may comprise a cyclic prefix of 0.4 ms and a guard time of 0.4 ms.

In certain embodiments, the narrowband PRACH slot may comprise at leastone narrowband PRACH segment. The method may comprise randomly selectingone of a plurality of possible narrowband random access preambles as thenarrowband random access preamble to generate, and randomly selectingone of the at least one narrowband PRACH segments for transmitting theselected one of the plurality of possible narrowband random accesspreambles.

In certain embodiments, the method may comprise determining a coveragelevel of the user equipment, and selecting, based on the determinedcoverage level of the user equipment, the narrowband PRACH format fromamong one or more narrowband PRACH formats. The coverage level of theuser equipment may comprise one or more of a basic coverage level, arobust coverage level, and an extreme coverage level. The method maycomprise repeating transmission of the narrowband random access preambleaccording to the selected narrowband PRACH format.

FIG. 6 is a flow diagram of a method 600 in a network node, inaccordance with certain embodiments. The method begins at step 604,where the network node configures, based on one or more criteria, anarrowband physical random access channel (PRACH) slot duration and anarrowband PRACH period for a narrowband random access procedure by auser equipment. In certain embodiments, the one or more criteria maycomprise one or more of: a cell load of a cell associated with thenetwork node; and a cell size of the cell associated with the networknode. The configured narrowband PRACH slot duration may be 12 ms. Thenarrowband PRACH slot may comprise at least one narrowband PRACHsegment.

At step 608, the network node receives, from the user equipment, anarrowband random access preamble via a narrowband PRACH according to anarrowband PRACH format, wherein the narrowband random access preamblecomprises a Zadoff-Chu sequence, and wherein the narrowband PRACH isfrequency multiplexed with a physical uplink shared channel (PUSCH) andcomprises: at least one narrowband PRACH slot having the configurednarrowband PRACH slot duration; and the configured narrowband PRACHperiod. In certain embodiments, the narrowband random access preamblemay be a Zadoff-Chu sequence of length 491. The narrowband PRACH maycomprise a subcarrier spacing of 312.5 Hz. In certain embodiments, thenarrowband PRACH may comprise at least one subcarrier guard band betweenthe narrowband PRACH and the PUSCH. The received narrowband randomaccess preamble may comprise a duration of 3.2 ms. The narrowband PRACHmay comprise a cyclic prefix of 0.4 ms and a guard time of 0.4 ms.

In certain embodiments, the method may comprise configuring the userequipment to randomly select one of a plurality of possible narrowbandrandom access preambles to generate. The method may comprise configuringthe user equipment to randomly select one of the at least one narrowbandPRACH segments for transmitting the selected one of the plurality ofpossible narrowband random access preambles. In certain embodiments, themethod may comprise determining the narrowband PRACH format according towhich the narrowband random access preamble was received. The method maycomprise determining a coverage level of the user equipment based on thedetermined narrowband PRACH format. The coverage level of the userequipment may comprise one or more of a basic coverage level, a robustcoverage level, and an extreme coverage level. The narrowband PRACHformat according to which the narrowband random access preamble wasreceived may be determined based on a number of repeat transmissions ofthe narrowband random access preamble. In certain embodiments, themethod may comprise scheduling the user equipment according to thedetermined coverage level of the user equipment.

FIG. 7 is a block schematic of an exemplary wireless device, inaccordance with certain embodiments. Wireless device 110 may refer toany type of wireless device communicating with a node and/or withanother wireless device in a cellular or mobile communication system.Examples of wireless device 110 include a mobile phone, a smart phone, aPDA (Personal Digital Assistant), a portable computer (e.g., laptop,tablet), a sensor, a modem, a machine-type-communication (MTC)device/machine-to-machine (M2M) device, laptop embedded equipment (LEE),laptop mounted equipment (LME), USB dongles, a D2D capable device, oranother device that can provide wireless communication. A wirelessdevice 110 may also be referred to as UE, a station (STA), a device, ora terminal in some embodiments. Wireless device 110 includes transceiver710, processor 720, and memory 730. In some embodiments, transceiver 710facilitates transmitting wireless signals to and receiving wirelesssignals from network node 115 (e.g., via antenna 740), processor 720executes instructions to provide some or all of the functionalitydescribed above as being provided by wireless device 110, and memory 730stores the instructions executed by processor 720.

Processor 720 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions ofwireless device 110, such as the functions of wireless device 110described above in relation to FIGS. 1-6 . In some embodiments,processor 720 may include, for example, one or more computers, one ormore central processing units (CPUs), one or more microprocessors, oneor more applications, one or more application specific integratedcircuits (ASICs), one or more field programmable gate arrays (FPGAs)and/or other logic.

Memory 730 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 730 includecomputer memory (for example, Random Access Memory (RAM) or Read OnlyMemory (ROM)), mass storage media (for example, a hard disk), removablestorage media (for example, a Compact Disk (CD) or a Digital Video Disk(DVD)), and/or or any other volatile or non-volatile, non-transitorycomputer-readable and/or computer-executable memory devices that storeinformation, data, and/or instructions that may be used by processor1020.

Other embodiments of wireless device 110 may include additionalcomponents beyond those shown in FIG. 7 that may be responsible forproviding certain aspects of the wireless device's functionality,including any of the functionality described above and/or any additionalfunctionality (including any functionality necessary to support thesolution described above). As just one example, wireless device 110 mayinclude input devices and circuits, output devices, and one or moresynchronization units or circuits, which may be part of the processor720. Input devices include mechanisms for entry of data into wirelessdevice 110. For example, input devices may include input mechanisms,such as a microphone, input elements, a display, etc. Output devices mayinclude mechanisms for outputting data in audio, video and/or hard copyformat. For example, output devices may include a speaker, a display,etc.

FIG. 8 is a block schematic of an exemplary network node, in accordancewith certain embodiments. Network node 115 may be any type of radionetwork node or any network node that communicates with a UE and/or withanother network node. Examples of network node 115 include an eNodeB, anode B, a base station, a wireless access point (e.g., a Wi-Fi accesspoint), a low power node, a base transceiver station (BTS), relay, donornode controlling relay, transmission points, transmission nodes, remoteRF unit (RRU), remote radio head (RRH), multi-standard radio (MSR) radionode such as MSR BS, nodes in distributed antenna system (DAS), O&M,OSS, SON, positioning node (e.g., E-SMLC), MDT, or any other suitablenetwork node. Network nodes 115 may be deployed throughout network 100as a homogenous deployment, heterogeneous deployment, or mixeddeployment. A homogeneous deployment may generally describe a deploymentmade up of the same (or similar) type of network nodes 115 and/orsimilar coverage and cell sizes and inter-site distances. Aheterogeneous deployment may generally describe deployments using avariety of types of network nodes 115 having different cell sizes,transmit powers, capacities, and inter-site distances. For example, aheterogeneous deployment may include a plurality of low-power nodesplaced throughout a macro-cell layout. Mixed deployments may include amix of homogenous portions and heterogeneous portions.

Network node 115 may include one or more of transceiver 810, processor820, memory 830, and network interface 840. In some embodiments,transceiver 810 facilitates transmitting wireless signals to andreceiving wireless signals from wireless device 110 (e.g., via antenna850), processor 820 executes instructions to provide some or all of thefunctionality described above as being provided by a network node 115,memory 830 stores the instructions executed by processor 820, andnetwork interface 840 communicates signals to backend networkcomponents, such as a gateway, switch, router, Internet, Public SwitchedTelephone Network (PSTN), core network nodes or radio networkcontrollers 130, etc.

Processor 820 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions ofnetwork node 115, such as those described above in relation to FIGS. 1-6above. In some embodiments, processor 820 may include, for example, oneor more computers, one or more central processing units (CPUs), one ormore microprocessors, one or more applications, and/or other logic.

Memory 830 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 830 includecomputer memory (for example, Random Access Memory (RAM) or Read OnlyMemory (ROM)), mass storage media (for example, a hard disk), removablestorage media (for example, a Compact Disk (CD) or a Digital Video Disk(DVD)), and/or or any other volatile or non-volatile, non-transitorycomputer-readable and/or computer-executable memory devices that storeinformation.

In some embodiments, network interface 840 is communicatively coupled toprocessor 820 and may refer to any suitable device operable to receiveinput for network node 115, send output from network node 115, performsuitable processing of the input or output or both, communicate to otherdevices, or any combination of the preceding. Network interface 840 mayinclude appropriate hardware (e.g., port, modem, network interface card,etc.) and software, including protocol conversion and data processingcapabilities, to communicate through a network.

Other embodiments of network node 115 may include additional componentsbeyond those shown in FIG. 8 that may be responsible for providingcertain aspects of the radio network node's functionality, including anyof the functionality described above and/or any additional functionality(including any functionality necessary to support the solutionsdescribed above). The various different types of network nodes mayinclude components having the same physical hardware but configured(e.g., via programming) to support different radio access technologies,or may represent partly or entirely different physical components.

FIG. 9 is a block schematic of an exemplary radio network controller orcore network node 130, in accordance with certain embodiments. Examplesof network nodes can include a mobile switching center (MSC), a servingGPRS support node (SGSN), a mobility management entity (MME), a radionetwork controller (RNC), a base station controller (BSC), and so on.The radio network controller or core network node 130 includes processor920, memory 930, and network interface 940. In some embodiments,processor 920 executes instructions to provide some or all of thefunctionality described above as being provided by the network node,memory 930 stores the instructions executed by processor 920, andnetwork interface 940 communicates signals to any suitable node, such asa gateway, switch, router, Internet, Public Switched Telephone Network(PSTN), network nodes 115, radio network controllers or core networknodes 130, etc.

Processor 920 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions of theradio network controller or core network node 130. In some embodiments,processor 920 may include, for example, one or more computers, one ormore central processing units (CPUs), one or more microprocessors, oneor more applications, and/or other logic.

Memory 930 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 930 includecomputer memory (for example, Random Access Memory (RAM) or Read OnlyMemory (ROM)), mass storage media (for example, a hard disk), removablestorage media (for example, a Compact Disk (CD) or a Digital Video Disk(DVD)), and/or or any other volatile or non-volatile, non-transitorycomputer-readable and/or computer-executable memory devices that storeinformation.

In some embodiments, network interface 940 is communicatively coupled toprocessor 920 and may refer to any suitable device operable to receiveinput for the network node, send output from the network node, performsuitable processing of the input or output or both, communicate to otherdevices, or any combination of the preceding. Network interface 940 mayinclude appropriate hardware (e.g., port, modem, network interface card,etc.) and software, including protocol conversion and data processingcapabilities, to communicate through a network.

Other embodiments of the network node may include additional componentsbeyond those shown in FIG. 9 that may be responsible for providingcertain aspects of the network node's functionality, including any ofthe functionality described above and/or any additional functionality(including any functionality necessary to support the solution describedabove).

FIG. 10 is a block schematic of an exemplary wireless device, inaccordance with certain embodiments. Wireless device 110 may include oneor more modules. For example, wireless device 110 may include adetermining module 1010, a communication module 1020, a receiving module1030, an input module 1040, a display module 1050, and any othersuitable modules. Wireless device 110 may perform the methods for NBPRACH design described above with respect to FIGS. 1-6 .

Determining module 1010 may perform the processing functions of wirelessdevice 110. For example, determining module 1010 may generate anarrowband random access preamble for a narrowband random accessprocedure, the narrowband random access preamble comprising a Zadoff-Chusequence. As another example, determining module 1010 may randomlyselect one of a plurality of possible narrowband random access preamblesas the narrowband random access preamble to generate. As still anotherexample, determining module 1010 may randomly select one of the at leastone narrowband PRACH segments for transmitting the selected one of theplurality of possible narrowband random access preambles. As yet anotherexample, determining module 1010 may determine a coverage level forwireless device 110. As yet another example, determining module 1010 mayselect, based on the determined coverage level of wireless device 110,the narrowband PRACH format from among one or more narrowband PRACHformats. Determining module 1010 may include or be included in one ormore processors, such as processor 720 described above in relation toFIG. 7 . Determining module 1010 may include analog and/or digitalcircuitry configured to perform any of the functions of determiningmodule 1010 and/or processor 720 described above. The functions ofdetermining module 1010 described above may, in certain embodiments, beperformed in one or more distinct modules.

Communication module 1020 may perform the transmission functions ofwireless device 110. For example, communication module 1020 maytransmit, to a network node, the generated narrowband random accesspreamble via a narrowband PRACH according to a narrowband PRACH, whereinthe narrowband PRACH is frequency multiplexed with a PUSCH andcomprises: at least one narrowband PRACH slot having a narrowband PRACHslot duration; and a narrowband PRACH period. As another example,communication module 1020 may repeat transmission of the narrowbandrandom access preamble according to the selected narrowband PRACHformat. Communication module 1020 may transmit messages to one or moreof network nodes 115 of network 100. Communication module 1020 mayinclude a transmitter and/or a transceiver, such as transceiver 710described above in relation to FIG. 7 . Communication module 1020 mayinclude circuitry configured to wirelessly transmit messages and/orsignals. In particular embodiments, communication module 1020 mayreceive messages and/or signals for transmission from determining module1010. In certain embodiments, the functions of communication module 1020described above may be performed in one or more distinct modules.

Receiving module 1030 may perform the receiving functions of wirelessdevice 110. Receiving module 1030 may include a receiver and/or atransceiver, such as transceiver 710 described above in relation to FIG.7 . Receiving module 1030 may include circuitry configured to wirelesslyreceive messages and/or signals. In particular embodiments, receivingmodule 1030 may communicate received messages and/or signals todetermining module 1010.

Input module 1040 may receive user input intended for wireless device110. For example, the input module may receive key presses, buttonpresses, touches, swipes, audio signals, video signals, and/or any otherappropriate signals. The input module may include one or more keys,buttons, levers, switches, touchscreens, microphones, and/or cameras.The input module may communicate received signals to determining module1010.

Display module 1050 may present signals on a display of wireless device110. Display module 1050 may include the display and/or any appropriatecircuitry and hardware configured to present signals on the display.Display module 1050 may receive signals to present on the display fromdetermining module 1010.

Determining module 1010, communication module 1020, receiving module1030, input module 1040, and display module 1050 may include anysuitable configuration of hardware and/or software. Wireless device 110may include additional modules beyond those shown in FIG. 10 that may beresponsible for providing any suitable functionality, including any ofthe functionality described above and/or any additional functionality(including any functionality necessary to support the various solutionsdescribed herein).

FIG. 11 is a block schematic of an exemplary network node 115, inaccordance with certain embodiments. Network node 115 may include one ormore modules. For example, network node 115 may include determiningmodule 1110, communication module 1120, receiving module 1130, and anyother suitable modules. In some embodiments, one or more of determiningmodule 1110, communication module 1120, receiving module 1130, or anyother suitable module may be implemented using one or more processors,such as processor 820 described above in relation to FIG. 8 . In certainembodiments, the functions of two or more of the various modules may becombined into a single module. Network node 115 may perform the methodsfor NB LTE PRACH design described above with respect to FIGS. 1-6 .

Determining module 1110 may perform the processing functions of networknode 115. As one example, determining module 1110 may configure, basedon one or more criteria, a narrowband PRACH slot duration and anarrowband PRACH period for a narrowband random access procedure by auser equipment. As another example, determining module 1110 mayconfigure the user equipment to randomly select one of a plurality ofpossible narrowband random access preambles to generate. As stillanother example, determining module 1110 may configure the userequipment to randomly select one of the at least one narrowband PRACHsegments for transmitting the selected one of the plurality of possiblenarrowband random access preambles. As yet another example, determiningmodule 1120 may determine the narrowband PRACH format according to whichthe narrowband random access preamble was received. As yet anotherexample, determining module 1120 may determine a coverage level of theuser equipment based on the determined narrowband PRACH format. As yetanother example, determining module 1120 may schedule the user equipmentaccording to the determined coverage level of the user equipment.Determining module 1110 may include or be included in one or moreprocessors, such as processor 820 described above in relation to FIG. 8. Determining module 1110 may include analog and/or digital circuitryconfigured to perform any of the functions of determining module 1110and/or processor 820 described above. The functions of determiningmodule 1110 may, in certain embodiments, be performed in one or moredistinct modules. For example, in certain embodiments some of thefunctionality of determining module 1110 may be performed by anallocation module.

Communication module 1120 may perform the transmission functions ofnetwork node 115. Communication module 1120 may transmit messages to oneor more of wireless devices 110. Communication module 1120 may include atransmitter and/or a transceiver, such as transceiver 810 describedabove in relation to FIG. 8 . Communication module 1120 may includecircuitry configured to wirelessly transmit messages and/or signals. Inparticular embodiments, communication module 1120 may receive messagesand/or signals for transmission from determining module 1110 or anyother module.

Receiving module 1130 may perform the receiving functions of networknode 115. As one example, receiving module 1130 may receive, from theuser equipment, a narrowband random access preamble via a narrowbandPRACH according to a narrowband PRACH format, wherein the narrowbandrandom access preamble comprises a Zadoff-Chu sequence, and wherein thenarrowband PRACH is frequency multiplexed with a PUSCH and comprises: atleast one narrowband PRACH slot having the configured narrowband PRACHslot duration; and the configured narrowband PRACH period. Receivingmodule 1130 may receive any suitable information from a wireless device.Receiving module 1130 may include a receiver and/or a transceiver, suchas transceiver 810 described above in relation to FIG. 8 . Receivingmodule 1130 may include circuitry configured to wirelessly receivemessages and/or signals. In particular embodiments, receiving module1130 may communicate received messages and/or signals to determiningmodule 1110 or any other suitable module.

Determining module 1110, communication module 1120, and receiving module1130 may include any suitable configuration of hardware and/or software.Network node 115 may include additional modules beyond those shown inFIG. 11 that may be responsible for providing any suitablefunctionality, including any of the functionality described above and/orany additional functionality (including any functionality necessary tosupport the various solutions described herein).

Modifications, additions, or omissions may be made to the systems andapparatuses described herein without departing from the scope of thedisclosure. The components of the systems and apparatuses may beintegrated or separated. Moreover, the operations of the systems andapparatuses may be performed by more, fewer, or other components.Additionally, operations of the systems and apparatuses may be performedusing any suitable logic comprising software, hardware, and/or otherlogic. As used in this document, “each” refers to each member of a setor each member of a subset of a set.

Modifications, additions, or omissions may be made to the methodsdescribed herein without departing from the scope of the disclosure. Themethods may include more, fewer, or other steps. Additionally, steps maybe performed in any suitable order.

Although this disclosure has been described in terms of certainembodiments, alterations and permutations of the embodiments will beapparent to those skilled in the art. Accordingly, the above descriptionof the embodiments does not constrain this disclosure. Other changes,substitutions, and alterations are possible without departing from thespirit and scope of this disclosure, as defined by the following claims.

Abbreviations used in the preceding description include:

AP Access Point

BS Base Station

BSC Base Station Controller

BTS Base Transceiver Station

CIoT Cellular Internet of Things

CP Cyclic Prefix

CPE Customer Premises Equipment

D2D Device-to-device

DAS Distributed Antenna System

DL Downlink

eNB evolved Node B

FDD Frequency Division Duplex

GERAN GSM/EDGE Radio Access Network

GT Guard Time

GSM Global System for Mobile communications

IoT Internet of Things

LAN Local Area Network

LEE Laptop Embedded Equipment

LME Laptop Mounted Equipment

LTE Long Term Evolution

M2M Machine-to-Machine

MAN Metropolitan Area Network

MCE Multi-cell/multicast Coordination Entity

MSR Multi-standard Radio

NAS Non-Access Stratum

NB Narrowband

OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PRACH Physical Random Access Channel

PSTN Public Switched Telephone Network

PUSCH Physical Uplink Shared Channel

PUCCH Physical Uplink Control Channel

RB Resource Block

RNC Radio Network Controller

RRC Radio Resource Control

RRH Remote Radio Head

RRU Remote Radio Unit

TDD Time Division Duplex

UE User Equipment

UL Uplink

WAN Wide Area Network

The invention claimed is:
 1. A method in a user equipment, comprising:determining a coverage level of the user equipment, selecting aconfiguration of a time-frequency narrowband physical random accesschannel (PRACH) resource, determining, based on the determined coveragelevel of the user equipment, a number of repetitions for a narrowbandrandom access preamble, transmitting, to a network node, a narrowbandrandom access message via said PRACH resource, wherein the narrowbandrandom access message includes a repetition of the same said narrowbandrandom access preamble according to the determined number ofrepetitions, wherein the narrowband PRACH resource is frequencymultiplexed with a narrowband physical uplink shared channel (PUSCH). 2.The method of claim 1, wherein the coverage level of the user equipmentcomprises one or more of a basic coverage level, a robust coveragelevel, and an extreme coverage level.
 3. The method of claim 1, whereinthe repetitions of the same narrowband random access preamble aretransmitted consecutively.
 4. The method of claim 1, wherein thenarrowband PRACH resource has a narrowband PRACH slot duration and anarrowband PRACH period, wherein the narrowband PRACH slot duration andthe narrowband PRACH period are based on one or both of: a cell load ofa cell associated with the network node; and a cell size of the cellassociated with the network node.
 5. A method in a network node,comprising: configuring a configuration of one or more time-frequencyphysical random access channel (PRACH) resources based on coveragelevels of a plurality user equipments served by the network node,receiving, from a user equipment, a narrowband random access message viaone of the narrowband PRACH resources, wherein the narrowband randomaccess message includes a repetition of the same narrowband randomaccess preamble according to a selected number of repetitions which isdetermined based on the coverage level, wherein the one or moretime-frequency PRACH resources are frequency multiplexed with a PUSCH.6. The method of claim 5, wherein the coverage level of the userequipment comprises one or more of a basic coverage level, a robustcoverage level, and an extreme coverage level.
 7. The method of claim 5,the repetitions of the same narrowband random access preamble arereceived consecutively.
 8. The method of claim 5, wherein each of theone or more time-frequency narrowband PRACH resources has a narrowbandPRACH slot duration and a narrowband PRACH period, wherein thenarrowband PRACH slot duration and the narrowband PRACH period are basedon one or both of: a cell load of a cell associated with the networknode; and a cell size of the cell associated with the network node. 9.The method of claim 5, wherein the number of times the narrowband randomaccess preamble is repeated is based on a determined coverage level ofthe user equipment, the coverage level of the user equipment comprisingone or more of a basic coverage level, a robust coverage level, and anextreme coverage level.
 10. A user equipment, comprising: one or moreprocessors, the one or more processors configured to: determine acoverage level of the user equipment, select, based on the determinedcoverage level of the user equipment, a configuration of atime-frequency narrowband physical random access channel (PRACH)resource, determine, based on the determined coverage level of the userequipment, a number of repetitions for a narrowband random accesspreamble, transmit, to a network node, a narrowband random accessmessage via said PRACH resource, wherein the narrowband random accessmessage includes a repetition of the same said narrowband random accesspreamble according to the selected number of repetitions, wherein thenarrowband PRACH resource is frequency multiplexed with a narrowbandphysical uplink shared channel (PUSCH).
 11. The user equipment of claim10, wherein the coverage level of the user equipment comprises one ormore of a basic coverage level, a robust coverage level, and an extremecoverage level.
 12. The user equipment of claim 10, wherein therepetitions of the same narrowband random access preamble aretransmitted consecutively.
 13. The user equipment of claim 10, whereinthe narrowband PRACH resource is frequency multiplexed with a narrowbandPUSCH.
 14. The user equipment of claim 10, wherein the narrowband PRACHresource has a narrowband PRACH slot duration and a narrowband PRACHperiod, wherein the narrowband PRACH slot duration and the narrowbandPRACH period are based on one or both of: a cell load of a cellassociated with the network node; and a cell size of the cell associatedwith the network node.
 15. A network node, comprising: one or moreprocessors, the one or more processors configured to: configure one ormore time-frequency physical random access channel (PRACH) resourcesbased on coverage levels of a plurality user equipments served by thenetwork node, receive, from a user equipment, a narrowband random accessmessage via one of the narrowband PRACH resources, wherein thenarrowband random access message includes a repetition of the samenarrowband random access preamble according to a selected number ofrepetitions which is determined based on the coverage level, wherein theone or more time-frequency PRACH resources are frequency multiplexedwith a PUSCH.
 16. The network node of claim 15, the repetitions of thesame narrowband random access preamble are received consecutively. 17.The network node of claim 15, wherein each of the one or moretime-frequency narrowband PRACH resources has a narrowband PRACH slotduration and a narrowband PRACH period, wherein the narrowband PRACHslot duration and the narrowband PRACH period are based on one or bothof: a cell load of a cell associated with the network node; and a cellsize of the cell associated with the network node.
 18. The network nodeof claim 15, wherein the number of times the narrowband random accesspreamble is repeated is based on a determined coverage level of the userequipment, the coverage level of the user equipment comprising one ormore of a basic coverage level, a robust coverage level, and an extremecoverage level.